Federal and state governments have enacted increasingly stringent laws and regulations on motor vehicle exhaust emissions and fuel economy. In one example, the state of California's regulations include Super Ultra Low Emission Vehicle (SULEV) emission standards, which are particularly stringent on hydrocarbon (HC) and nitrogen oxides (NOx) emissions. As this trend continues, Zero Emission Vehicle (ZEV) standards can eventually become enacted.
In order to meet these increasingly stringent emission requirements, motor vehicle manufacturers can employ exhaust treatment systems that are capable of reducing both gaseous and particulate emissions (e.g., NOx gases, carbon monoxide). These exhaust treatment systems can comprise devices such as catalytic converters, selective catalytic reduction catalysts, and the like, that are capable of reducing the undesirable gaseous constituents (e.g., hydrocarbons, carbon monoxide, NOx) by converting the gases into less-undesirable emissions (e.g., carbon dioxide, water, nitrogen). In concert with devices, particulate filters can be employed to remove hydrocarbon particulate (e.g., soot) from an exhaust stream by trapping the particulate on and/or within a porous substrate and periodically oxidizing the hydrocarbon particulate at elevated temperatures.
Although exhaust systems employing gaseous and particulate remediation devices have proven successful, their cost is inhibitive due to costly catalysts (e.g., platinum, palladium, rhodium) employed therein. This is of concern to consumers and motor vehicle manufacturers as system costs can increase sharply with each proposed emission standard. Therefore, there is a need for innovations in internal combustion engine systems (e.g., spark ignition, compression ignition) that are capable of decreasing the mass of undesirable emissions produced and decreasing the cost and dependence on catalyst-based exhaust after-treatment systems.